Denis Schneider

Investigation of Combustion Oscillations in a Lean Gas Turbine Model Combustor

This contribution is a continuation of ASME-GT2006-90300. While still working at atmospheric pressure, the range of operating conditions was extended to more realistic reduced mass flows to reproduce the engine pressure loss and air preheat up to 700K. The thermoacoustic behaviour of the burner was mapped over that operating range. Two different types of oscillations were observed for flames anchored at the nozzle or lifted from it. Both exhibited a frequency dependence on the Strouhal number for constant reduced mass flows. For a selected operating point with the lifted flame at a preheat temperature of 600K and a reduced mass flow of 0.3kg K0.5/(s bar), the thermoacoustic behaviour of the burner was characterised by phase locked Particle Image Velocimetry as well as phase locked OH- and OH-T- LIF measurements and correlated to the acoustic pressure signal obtained by microphones. The combined data showed pulsating combustion being supported through periodic reignition of the main flame zone by a recirculating volume of hot, OH-rich gas, the cycle time being connected to the observed frequency. The characterization of the preheated operating point was completed with a heat balance investigation quantifying the non-adiabatic combustion conditions of the uncooled combustor.

Effects of Fluidic Control of Air-Flow Distribution on Staged Lean Jet Engine Burner

In this study, the effects of air-flow shifting between the pilot and main stages of a staged lean jet engine burner were investigated. A fluidic element attached in front of the swirlers was used to alter the air-flow split ratio between them, and the swirler and nozzle exit-section pressure loss behind the fluidic element was measured using an atmospheric isothermal test. The fluidic element did not fully recover the pressure loss in the burner inlet. However, it can also affect the losses, and cause an air shift between the pilot and main stage. Therefore, further combustion tests were conducted under two operating conditions: ground idle at 7% maximum take-off thrust and scaled cruise condition. Under ground idle conditions, increased pilot air flow improved the combustion efficiency for high fuel flow, and reduced pilot air flow improved it for low fuel flow. Staged and unstaged operations were also investigated under cruise conditions. In the staged operation, reduced pilot air flow increased the combustion efficiency, whereas in the unstaged operation, greater pilot air flow increased the combustion efficiency near the fueling mode switch-over point.

Characterization of a Real Size Retrofittable Catalytic Combustion System

This contribution describes the investigation of an engine-scale catalytic hybrid burner. The burner has been investigated under atmospheric conditions with preheated air and natural gas fuel in two operating points, with and without the catalytic reactor. By using the catalyst, an extension of the operating range to leaner stoichiometries has been demonstrated. Exhaust gas analysis performed directly downstream of the burner as well as in the burner far-field showed a NOx reduction potential of more than 20% when employing the catalyst. For the operation with the catalytic reactor, the flame stabilization process and dependency of NOx formation on the piloting gas ratio is described with results of OH chemiluminescence measurements. Radial temperature profiles taken with Coherent Anti Stokes Raman Scattering (CARS) suggest a reaction delay directly downstream of the catalytic section of the burner. Calculations with a perfectly stirred reactor model help to obtain a better understanding of the kinetics of the hot gases leaving the catalyst section.Copyright